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Real-Time Position Management (RPM) System as a Valuable Tool to Predict Tumor Position Deviation in SBRT Lung and Liver Patients with Breath Hold Using Active Breathing Coordinator (ABC)

Z Shen

Z Shen*, M Andrews , S Balik , A Magnelli , K Stephans , G Videtic , M Abazeed , T Zhuang , P Xia , The Cleveland Clinic Foundation, Cleveland, OH


SU-F-J-141 (Sunday, July 31, 2016) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: ABC is a breath-hold technique for SBRT treatments. At our institution, three CTs with ABC are acquired at simulation to check the breath-hold consistency because tumor position may deviate among three scans. The purpose of this study was to determine whether RPM can predict tumor position deviation in SBRT breath-hold treatments with ABC.

Methods: Five SBRT lung and five SBRT liver patients were selected. An RPM block was placed on the patients between the xiphoid and the umbilicus. RPM recorded patients’ anterior-posterior skin surface positions during breath holds with ABC. For each patient, three CTs (ABC1, ABC2, ABC3) were acquired at the same breath-hold level. ABC2 and ABC3 CTs were rigidly registered to ABC1 CT. Tumor position deviations were measured on the fused CTs (ABC2 with ABC1, ABC3 with ABC1) and compared to the corresponding RPM position shifts. Linear regression, k-means clustering, and decision tree classifier were used to determine the relationship between RPM position shifts and tumor position deviations.

Results: Tumor position deviations were 0.4-8.7 mm for lung patients and 1.6-9.1 mm for liver patients. There were no significant linear correlations between RPM position shifts and tumor position deviations for both lung (R²=0.20) and liver (R²=0.45) patients. In contrast, decision tree classification showed that the RPM position shift of 3.45 mm or more indicated tumor position deviation >5 mm for lower lobe lung tumors and liver tumors that are close to the diaphragm.

Conclusion: RPM position shifts are not linearly correlated with tumor position deviations. However, RPM can be used to predict large tumor position deviations (>5 mm) among three ABC CTs in SBRT for lower lobe lung tumors and liver tumors and to validate the breath-hold consistency with the ABC technique. Therefore, RPM has the potential to replace the additional verification CT scans.

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